Monthly Archives: June 2015

Making your GSX frame stiffer
Written by Mr.7/11, inspired on earlier work done by Tony Foale, Arnout and Tinus.

It may be well known to anybody that creating a stiff frame has to do with connecting the headstock to the swingarm pivot as direct as possible, which is what modern “Deltabox” frame designs do. So the best possible solution is to weld f*cking huge bars from the headstock directly to the swingarm pivots. There is just one problem with that… there’s a huge mother of an air-cooled engine in between that hasn’t followed any diet …ever.

To keep the weight down we remove some before adding any.

And besides she’s so beautifully shaped that we wouldn’t want anything hiding those luscious curves from full view now would we? So we’ll have to resort to beefing up the frame we have as well as possible so the front wheel will keep in line with the rear during heavy braking/acceleration as well as big bumps in the road.

The GSX frame is of the “cradle” type which means the main frame tubes are routed above and below the engine. We haven’t got many options for reinforcing the lower cradle as there are exhaust pipes, oil cooler lines and the oil sump between them and we don’t want to create problems while performing regular maintenance.
So we leave it alone with it’s primary task to keep the engine in place concentrate on the part of the frame that runs above the engine.

Take a look at the picture below.
The weak point of the frame is the green section between the headstock (yellow) and the swingarm pivot area (blue). If you look at early GSX-R frame designs you see that on race bikes they have allways tried to beef up that area with additional plates. There’s also a rumour this is what Yoshimura used to do with their GSX superbikes. Suzuki have allready paid lots of attention into making the headstock as stiff as possible so the effect of additional bracing here will be minimal. If you intend too keep the standard airbox and the battery in it’s original place then options for bracing around the swingarm pivot will be minimal too. So if you would like ot improve the stiffness of your old dinosaur I’d make modification C. first, and consider dumping the airbox in favor of separate K&N filters to be able to add D. and E. When you’re at it you might as well go along and add braces A. and B. but I don’t consider them to be essential.

Be warned that reinforcement C. can hit the inside of the tank if you make it too big and will also make it hard to find enough space for the air filters! You should make all reinforcements from cardboard first anyway to check that they don’t interfere with anything.

A. these tubes support the headstock against torsional movement. The plates B. support the frame tubes to prevent them from bending due to the load created by tubes A.

The cross-bars D. stiffen the area above the swingarm pivots. The tube connecting both sided is placed at the same height as the engine mounts to keep the engine in place under acceleration. If we replace the cross-bars with a pyramid D1. we add even more stiffness to that area and prevent the swingarm pivots from moving back and forth in addition to up and down. It may look a bit awkward and I question if it adds anything as you must not underestimate the strength and function of the rear subframe.This might be why Yoshimura adds gussets to the subframe on the Katana 1135R, but they have also changed position of the shock mounts considerably. They probably did this because they use a very short swingarm to decrease the wheelbase and so improve steering into corners and if they kept the original mounting point the shock would be too upright making them too hard.

Examples of frame braces on the Yoshimura Katana 1135R

The connecting rectangular tubes E. help to distribute loads from the swingarm pivots to the rear of the frame, as well as providing a mounting point for the rear brake amongst other things.

F. There’s very little room to triangulate the space in front of the cylinders because of the exhaust pipes but it is possible. You may need to dent the tubes a little to make them clear the exhaust pipes but this is better than making the V smaller. Tightening the two center exhaust clamps will prove difficult too.

Below are drawings of engine mounts to fit an early air-cooled GSX (round frame tubes) or EFE (square frame tubes) with a GSX-R engine. Both place the engine in the middle which is aesthetically best but may cause some problems with the exhaust headers interfering with the frame downtubes, which can be solved by using spacers or modifying the headers if necessary.Engine mounts for a GSX1100 frame to take a GSX-R engine.By “jonboy”

A Katana with the above engine mounts installed…

Engine mounts for a GSX1100EFE (GS1150) to take a GSX-R engine.
By “GJG”

Below are drawings from the engine mounts, as I used them a few years back. I built at least two EFE’s using these plates. They mount the engine pretty straightforward, like in the Katana I send you pics from a few months back. I also included the cutting contours in .dxf format, that could straight be fed into a laser.

PL-107 and 108: These should be welded in with the engine or cases in place, mounted with the previous mentioned plates. PL-108 is a bit long, and could do with a brace, taking sideward loads to the cross tube from the shock. The stock plate should be removed. The lower cross tube in the frame will need some cleaning up and removing of the stock lower rear plates, before taking PL-107.

PL-110 and 111: These make the removable, welded upper rear engine mount taking loads to the stock bolt holes/bushings welded into the side of the frame.

First you remove the cover from the bike ofcourse, and then you degrease it very thoroughly.

As with all cracks in every material you need to drill small holes at the end of the cracks. Do not drill exactly at the point where the visible crack stops because underneath the surface the crack already had gone further. So plot an imaginative line in the extent of the crack and drill the hole along that line a few millimeters from the end of the visible crack.

I used a Dremel tool, but you can use a normal drill with a grinding stone (though due to it’s weight it’s harder to control) to dig a trench along the crack.
Dig as deep until you’re almost coming trough on the other side. This will make it very easy to fill it with epoxy.

Clean the other (in)side using emery paper or a Dremel tool to make sure the epoxy will attach itself well.

Then you clean and degrease the cover very thoroughly and warm it up by laying it on a heat source like a radiator or geyser.

While the case is heating up we prepare the metal epoxy. I use “Bison” metal epoxy but I guess any well known brand metal epoxy will do just fine. Just follow the instructions that came with it carefully and be sure to mix it very thoroughly. As with all two-component substances mixing it thoroughly is most important, so don’t rush it!

When the epoxy is ready apply it to the cover. Make sure you push the cracks full of epoxy so no air bubbles are left in them. If you dug them out deep enough epoxy will come out on the others side.
Your cover will have a very large flat spot so be sure to apply enough material, better too much than too little.
Apply some epoxy to the inside too but it hasn’t have to be much, just enough to make it smooth.

Then you leave it to dry on a heat source, at least for 12h untill the epoxy has become very hard. It hasn’t got the same mechanical properties as aluminium though, more like a hard plastic.

Now you can file/sand it into shape and spray paint the cover (you didn’t intend to polish it, now would ya? 😉

Well, there you are… a good as new engine cover, ready to last untill the next crash!